


The Advanced Dating Manual

by Get Dunked On (LittleKnownArtist), LittleKnownArtist



Category: Undertale (Video Game)
Genre: Bitemarks, Biting, Bruises, Cherryberry - Freeform, Consent is key, Dom blue, Double Penetration, Ecto-Genitalia (Undertale), Ecto-Tongue (Undertale), Explicit Sexual Content, Kinda?, Light Bondage, M/M, Rough Sex, Sexual Content, Shibari, Underfell Sans (Undertale), Underswap Sans (Undertale), and wow if he didn't get it, do fingers count?, red asked for it, sub Red
Language: English
Status: Completed
Published: 2019-11-09
Updated: 2020-01-15
Packaged: 2021-01-22 23:23:45
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 3,662
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21310330
Author URL: https://archiveofourown.org/users/LittleKnownArtist/pseuds/Get%20Dunked%20On, https://archiveofourown.org/users/LittleKnownArtist/pseuds/LittleKnownArtist
Summary: Red didn't understand Blue at all. He was spunky, overall happy-go-lucky, energetic and innocent. He hated it. He wanted nothing more than to corrupt that innocence.Except. Maybe Blue didn't need Red to corrupt him. Maybe Red didn't know what he was getting into.
Relationships: CherryBerry, Sans/Sans (Undertale), Underfell Sans/Underswap Sans
Comments: 26
Kudos: 212





	1. What Is Advanced Dating, Exactly?

**Author's Note:**

> I was considering adding a dubcon warning because Red didn't know what he signed up for but I don't think it actually needs it?
> 
> I really wanted to write a dom/top Blue because he's the energetic one. Also multiple male orgasms isn't typically something I'm into because it's unrealistic, but they're magic. Biology can jump the shark.

**Notes for the Chapter:**

> Prematurely posted chapter 2. Ignore that, it's still in the Hot Mess phase.

Red didn't understand the little guy at all. Well, the little guy was actually an inch taller than him, but that was beside the point. He was spunky, overall happy-go-lucky, energetic and childlike. He didn't exactly act like his 20 years, and for some reason...Some reason...Red hated that. There was something inside him that wanted to corrupt that innocence. He wanted to defile him in all his naivety. He couldn't do quite that, as gross as he was, he wasn't the type of monster that had it in him to force Blue--or face the wrath of Stretch or his own bro, who enjoyed discussing puzzle schematics with him. But. If the little guy consented to his own defilement, no one could argue, could they?

Convincing him to 'date' Red had been easy enough. The little sugar plum fairy had asked him, several times, though Red was certain he didn't understand the logistics of dating. He'd asked an 8-year-old for a date, after all. So sure, he'd 'date' the guy. Red had made sure Stretch was busy, but he hadn't expected that the little bubbly bastard would immediately take Red to his room.

"I've learned a lot more about dating recently, but the Dating Manual is still a great set of general guidelines," he boasted, tapping the cover of the book before setting it on his desk. "As such, I took you to a very special place! My room!"

Red smirked, cocking a browbone. He stepped forward, and Blue tilted his head as the sharp-toothed skeleton began to encroach on his personal space.

"oh? and what sortsa' things 'ave ya learned recently?" Red tapped his chest, allowing that finger to slide its way down the other's sternum.

"O-oh, well--" his cheekbones flushed with magic as he pondered the question.

"I have learned that it is best to take a date out to eat for the first date!" He swallowed, back hitting the wall. Red laid a hand on Blue's shoulder.

"Allowing them to indulge in home cooking is for when--" Red's fingers trailed along his collarbone, just above the hem of his croptop, "--you're sure you like them, and wish to reel them iiii~iiin!" The last syllable was squealed as Red gripped his jaw. He dipped forward and pressed his teeth against the other monster's. Blue went completely rigid in Red's grasp. He pulled away after swiping his tongue over Blue's stubbornly closed teeth. The little guy's eyelights were huge, sparkling with excited stars, but his entire face was flushed blue and his expression was stuck in shock. Red thought it was fucking hilarious.

"you seem nervous, pal. you wanted ta date me, right?" Red asked, raising a browbone as if he were confused.

"Uh. Kissing...kissing isn't supposed to be for the first date!" The giant blueberry blinked rapidly as he spoke. Red smiled. Stars he wanted to ruin this guy. To just fuck him up. Make him beg. He could already feel the magic starting to coalesce in his pelvis.

"uh-huh. here's the thing. i know that's prolly what the manual says, but i got a lil' more experience in datin' than you, so why don'tcha let me lead the way, eh? consider it 'advanced dating'. whatchu say?"

Blue was silent for a moment. Red stroked his jaw a little, hopefully distracting the guy from thinking the 'offer' over too much.

"...advanced dating?"

"that's the idea." Red blinked up at him attempting his best 'innocent-but-not-too-innocent' face.

"O-okay." That's all Red needed. He leaned forward to catch his mouth again. He laid a second kiss against his teeth when Blue seemed to reciprocate, pressing back and tilting his jaw slightly. Red's other hand wrapped around his ribs, phalanges brushing his spine. To his surprise, hesitant hands came up to his shoulder blades. The guy gasped when Red's thumb slipped between his teeth to gently pry his mouth open and slip his tongue inside. Blue whimpered against his mouth. Red's tongue brushed through magic in the moments it took to form into something solid. Blue's tongue was just as hesitant as his hands, in that soft, innocent, _pathetic_ way of his.

For a second.

Then he did something Red didn't expect in gently suckling on his tongue. The schematics on how he did that were a little fuzzy, but Red groaned lowly nonetheless. In a second unexpected turn, the once hesitant hands on his scapulae slid to Red's hips.

Oh wow. He must be...following his instincts or some shit. If he was doing that, he'd have this little bastard screaming his name by the time the underground's lights went out. His magic was already settled into place in anticipation. He was getting harder now that they were both breathing heavier.

For a third surprise, the hands on his hips slid lower. Red jolted a bit. His magic formed against Blue's probing hands, a vestigial entrance, when all Red really needed was his dick. Blue's hands then wrapped around his femurs and lifted him, startling him again as he was pressed to Blue's chest and his legs were wrapped around Blue's hips.

"huh?" Was all Red could ask when the other skeleton took three steps and deposited him onto his bed. He looked up, and Blue's face was hidden for the moment it took him to strip his croptop off. Red's eyelights were drawn to those smooth, unmarred, perfect white bones of his ribs. Blue hadn't had to fight for survival, hadn't tousled tooth and claw and magic for everything he had in life. He had it so easy. His world was so soft, he could grow up oblivious and smooth and _innocent_ and Red hated it. He was disgusted by this guy's childlike demeanor. His oblivious state of being. Red hated it so much. He remembered why he was here. He wanted to see the little bubbly bastard become a little less innocent. A little more aware. Wanted him flustered and begging. Craving his touches. Being everything but innocent.

A hard mouth was crushing against his again. This time, a tongue was exploring his mouth, running the tip against the edges of his fangs. That tongue was then against his jaw. There were more kisses.

"You were staring," Blue said between kisses, "I suppose that means you like what you see?"

_What?!_

Blue's voice had dropped so much lower than it usually was. His voice was teasing and thick, something which--which wasn't right for the taller skeleton. No. He wasn't supposed to--

Red found hard fingers prodding his ribs beneath his shirt. Stroking against them. He let out a surprised grunt. Fingers inside his rib cage, against the sensitive underside of his sternum.

"I thought so. You're the same as me." Blue's voice was so deep, so--what the hell?

He gave a startled yelp when his shirt was ripped off over his head in one fluid movement. Red was so caught off guard, his instincts were caught between playing dead and trying to get away. A hot breath was at his neck, a slippery tongue probing the sensitive discs between his cervical vertebrae, hands were roaming his lower spine and hips and all he could do was squirm.

Those hands were at the waistband of his shorts, thumbs dipped below it. Blue sat up then, and Red finally got a look at his face. He was grinning. The same grin as always, exuberant, excited; but something was different. Red didn't know what. His head wasn't working.

"Right." Blue slid his thumbs around the elastic waistband, "the Advanced Dating Manual says that consent is key, so, Red. Do you want this?"

He asked like he already knew the answer. And the answer was definitely yes. Was there really an advanced manual or was Blue just making shit up?

"i-i-yeah i do. stars, i do." He said this without thinking. His actual thoughts were a series of screeches and dial-up noises as he tried to process the last two minutes of his life.

Blue's grin grew wider, eyelights sparkling. He yanked the shorts down to Red's knees, cocking his head to the side when he caught sight of Red's magic, hard and proud.

"Hm." Was all he said as he lifted Red's legs and pulled his shorts completely off. His legs jerked when Blue gave a little tap to the tip of his dick. Blue trailed that finger down, and Red gave a little hiss.

"I don't have any lubrication," he said, as his finger trailed further. Red squeaked when it pressed against the entrance Red thought he wouldn't be using tonight.

"But if you're sure..." Red's mind finally caught up to the current situation as Blue unbuckled his belt, undid his shorts, and revealed a thick, hard coalesce of magic. Red was supposed to be corrupting Blue, but now he was certain that Blue fully intended on fucking him.

_"no lube?"_ Red thought with mild panic. He'd been around that block once before and he'd be the first to say that ghetto fucking sucked.

"h-hey," he started. There might be a chance to turn this around still. But then Blue leaned over him, pinning his wrists. He tried to lift them, but Blue was strong as fuck.

"Shh..." Blue soothed, "you're alright. Unless...you want to stop?"

Red blinked.

That was right. Red had gone into this for the sole purpose of sexing up the blueberry. He'd wanted to...well, he wanted to corrupt him. But now...it was quite clear that Blue wasn't quite as innocent as everyone thought. He was already corrupted, but he was calculating. He hid it well. And holy shit. Red didn't know what to think. But what the hell. Now that he knew this, he was still in prime position for a lay. How could Red turn that down? So it hadn't gone exactly as expected. What could it hurt to bottom for the sugar plum fairy?

Well, besides that.

"i don't wanna stop, just give me a sec," he replied. He focused on the magic in his pelvis, forcing the shape to something else. He sighed as it shifted. He felt liquid magic oozing. Lubrication wouldn't be an issue with how wet he felt down there

"Oh wow!" Blue's voice was nearly as bubbly as it was normally. Red flushed. Blue's gaze was suddenly drawn down to the dripping vulva he had formed.

"It's so pretty." He released one of Red's wrists to touch the solidified magic. He spread the outer lips, brushing Red's clit in the process. Red shivered.

"I've never seen one in person. Mn... definitely prettier on you than in a diagram. Look how wet you are." Blue chuckled, repositioning his body, slicking his blue cock up against Red.

Oh boy.

* * *

Red came to with his face pressed into a spot of his own drool and he realized he'd passed out again. He could feel the warmth of Blue's renewed release inside him and Red trembled again. Red lost count of how many times he'd come, but this had to be Blue's forth. What the fuck. That wasn't normal.

"Mng..." Blue moaned, giving a small buck of his hips, one hand squeezing painfully on the bruises to his trembling partner's illium, the other finally leaving his oversensative clit. He took a deep breath, sighing against Red's spine. He straightened up, running one hand from Red's skull down between his shoulder blades.

"As much as I would enjoy continuing this," he said, his voice still thick with lust in a way Red still never thought possible before tonight, "I do have work in the morning, and I find myself more productive when I sleep for several hours. Sorry, darling."

Red shivered at the feel of Blue pulling out, a thick dribble of cum following. Red couldn't move, stuck on his chest and knees until his partner rolled him over. He was limp as a ragdoll. Blue grinned down at him the way he always did, except now, Red could see the spark of depravity in those enlarged eyelights.

"Ah...look at you. You look absolutely _wrecked_. It's adorable." Red felt his face heat, and his gaze jerked away, but he didn't fight the complement. He couldn't fight anything right now. Blue leaned over him, hand cradling his mandible and nuzzling against his teeth.

"Did you enjoy yourself?"

Red gave a shallow nod.

"Good. Let's get you cleaned up, shall we?"

At the beginning of the night, Red had thought 'what could it hurt,' to bottom to a surprisingly dominant sugar puff. The next morning, he had his answer. Most of his body under his clothes were a smattering of bruises and bitemarks, and his pelvis had never before been this sore. Although he'd consented to the encounter, he hadn't realized how in over his head he had been. His legs were like jello and his magic was. Well. Confused? He didn't trust himself to walk, let alone teleport home, so Blue had deposited him on his own couch on his way to work. He left a bento for Red, so that he would have something for lunch which would help him 'regain his strength'.

Well. He'd need it.

But honestly what the hell happened last night? The phrase 'fucked your brains out' came to mind. He didn't have any brains, but if he had, they were scrambled and replaced with Blue's dick, because as he sat there flipping through channels for hours, the only thing he could think about was Blue, and specifically, his light blue cock.

Oh damn.

He was somewhat happy the little fucker had proven him wrong about his assumed innocence but. This was so fucled up. Red couldn't stand the guy's cheerful attitude. Yet...that was truly the best fuck he'd ever had. And if it was just an act..................


	2. If It Weren't For Meddling Brothers

**Summary for the Chapter:**

> Brother Shenanigans. Don't siblings just ruin all the fun?

**Notes for the Chapter:**

> Sorry it's so short and the writing quality is? whatever? I just wanted it done. Having it sit here as a WIP was KILLING ME.

Red had passed out there on the couch right where Blue had left him. Some hours later he was awoken to the sound of the door slamming and his Disgruntled Papyrus Noises. He opened his eyes to see his brother tapping his foot impatiently.

"what?"

"Don't you 'what' me. I told you that if you're going to nap all day to at least do it in your room." 

Red shrugged.

"Ugh! Well whatever, either get up and help me with dinner or go back to sleep in your room." Papyrus walked past the couch into the kitchen.

"'m i that unsightly, bro?"

"YES!" Papyrus shouted from the kitchen. Red snickered. He made a move to get up, but the sharp pain in his pelvis immediately made him regret the movement. He grunted sharply, falling back down on the couch where he had been sitting. His brother poked his head around the corner at the noise.

"What's wrong with you?"

Red chuckled.

"uh. it's not gonna be easy for me to move for a while here."

Papyrus quirked a browbone. Sans started to sweat with the unasked question.

"i um, kinda sore..." he mumbled something about Blue, and Papyrus must have heard some of it.

"Blue? OH! Did he finally get you to play basketball with him? I told him that encouragement from someone your own size might help you to become more active. Looks like your pathetic out-of-shape body wasn't up to snuff."

"...not sports, no..." 

Papyrus blinked twice. Then his face morphed into something between rage and horror.

"SANS!! TELL ME YOU DIDN'T? OH GOD. WHAT DID YOU DO TO HIM?" He came stomping over to Sans, hand fisting in his red sweater. Papyrus was very protective of his good friend. Red knew this. Papyrus had also known that Red had some...less than pure thoughts about his good friend, which thoroughly disgusted him. He never thought Red would actually get up the nerve to act on any of those thoughts though!

"i didn't do nothin'! bro!"

"IF YOU'RE SORE FROM--IF YOU HURT HIM, I SWEAR TO YOU--"

"no, no it's definitely not what you--okay, maybe it is but look. i was the one getting fucked within an inch of my life, okay?" and honestly, he hoped to have it happen again and again. He shifted though, and pain went back up his spine. Not for a few days, though.

"He? He...He was the one who..."

Red panicked. He got stupid when he panicked. His mouth ran ahead of his nonexistent brain.

"i've never been dicked so good in my life, honestly. baby blue's got stamina in spades." 

"EW!" Papyrus dropped him and shook his hand like he'd just touched rotten food.

"I DIDN'T NEED TO KNOW THAT!"

"you asked!" Red's cheekbones were burning hot. As if he hadn't just admitted to his activities freely.

"NO!"

"yes you did!"

"OH MY GOD!" Papyrus slapped his hands over his face, cheekbones flaring almost as hot as his elder brother's. He looked absolutely scandalized.

Papyrus screamed very quietly. His friend, small and pure, couldn't do that! Wouldn't do that! But his brother did have a good point about his stamina--Although! He had only ever seen his stamina during a sparring session. Of course he wouldn't know about! God! No!

Red screamed internally. 

"If you're lying and you hurt him--!"

"look!" Sans said, grabbing the bento from the table, and plucking the note from the lid. 'Thank you for the A M A Z I N G time! Make sure you eat everything, this will help you recover your strength.' Papyrus wanted to die. Red wanted to die. They didn't speak to each other for the rest of the day, although Papyrus set a bottle of pain medication beside a bottle of water for Red five minutes later.

* * *

As embarrassed as the whole debacle with his brother had made him, Blue had set up another date with him and Red...well, Red couldn't resist. This time Blue fed him before railing him int the mattress. Thrice.

They had some kinda weird thing going. Red's younger brother looked completely mortified when Blue helped Red through the door of their home after the date. Papyrus couldn't make eye contact with either, even as Blue greeted him in a chipper tone. Blue actually pulled red up the stairs into his room this time, so Papyrus didn't have to think about what went on. Out of sight, out of mind. Except, Papyrus still felt like bleaching the inside of his skull, hoping it would wash away the mental image of one of his best friends on top of his brother.

That was one brother. Blue's older brother--well. Red didn't even want Blue to mention that they were together. Together? Yeah, two dates and some sexcapades probably means that. Plus, he was...sort of starting to like the guy? He'd never really discussed his own interests with the guy, but sometimes after sex, when they were bathing, he'd get all sentimental. He mentioned his love for the stars, the moon. Even among monsters who had been underground their entire lives, the night sky held a special place in Red's soul. As it turned out, the same could be said for Blue. They got to talking about space travel, then and--Hell, they actually had a lot in common. Blue agreed that he really didn't want his brother to find out right away, either. He would have to break the news to Stretch eventually. Just, in a way that didn't get Red's legs blasted off. Blue decided to be the one to break the news, although he was still trying to think of the most gentle way possible. As it stood, Blue and Red made sure to come home from (or for?) their rendezvous only after Stretch had left the house.

Which worked for a little while...But Stretch wasn't an idiot. Not completely. Stars, Red hoped he wasn't alone with the guy when he finally figured it out. That being said...He still couldn't stay away from Blue. Because he *was* an idiot. And good dick made him more of an idiot. He still came to play with Blue when he offered, usually as soon as his brother left for work on weekends. Stars, he was treading dangerous waters.

He couldn't help but jump at the opportunity when Blue texted him one early morning. He was an idiot. The hugest idiot of the entirety of monsterkind. But damn. 

They had just gotten into some of the kinkier activities recently. Blue moaned aloud when Red had cum for a second time, clenching around the taller skeleton's cock. Red shuddered. They almost didn't notice the sound of something outside the door. They heard a clicking sound, but before they could even guess what it was, the door was thrown open and there was Stretch, shouting, a lockpick in his right hand.

"If you've hurt him you fucking piece of shit, I'll--"

And there the were. Red, with blue rope intricately woven around his ribs, tying his hands behind his back, red tears streaking down his cheeks from overstimulation. Blue, balls deep in Red's ass, three lefthand fingers shoved into his glowing red pussy, and his right hand gingerly tipping Red's chin. There they all were, three skeletons wearing the same looks of mortification and surprise. Red closed his legs, but it did nothing to cover the purple tinge to the magic in his pelvis, his partner's blue dick plainly visible through the translucent red of his own magic. His entire skull was coloring with flushed magic. 

"Papyrus...did you just pick my lock?" Blue said, as if that were the most important thing here. Stretch's eyelights glazed over and his face fell into expressionlessness, staring into nothing as he slowly backed out of he room.

"...my bad. I'll, uh, leave you guys...to it then?" He closed the door with a soft click. Five seconds passed in silence. 

"Red? You're really tight now. I think we should stop," Blue said, breaking that silence. 

"n...no shit," he squeaked.

**Author's Note:**

> I'm probably going to add a second chapter, but I'll call it complete in case I never get around to it.


End file.
